How much is the hand of God worth? At least $16,866 it seems, as that's where the bidding stands on eBay, and it will close at midnight tonight. Paul Grayhek of Idaho found the 9ft sacred shape in the rock wall at the end of his yard after a rock slide, and is selling it along with all movie and image rights, but not shipping.

Such apparitions are of course a mystery, starting with identification. How exactly do you tell the hand of God miraculously manifest in stone from the hand of, say, Adrian Chiles or Beyoncé? It has four fingers and a thumb, and that's about it for distinguishing features. What makes it God's?

Surely of all the possible candidates, anyone who actually has hands must be more likely than someone who, all major authorities agree, has no physical existence at all. Of course few people other than God can control the forces of nature so well as to create rock hands in this way. But should we really assume the Lord is so vain that the only portrait he would be interested in giving us is his own?

The question of identification goes for others who commonly feature in apparitions too. The Virgin Mary has appeared to the faithful in recent years in a cheese toastie, a salt stain in an underpass, drippings in a chocolate factory, and chemical deposits on a hospital window.

She tends, to be fair, towards the indistinct, and is only recognised by her headwear. This means it's hard to be certain that the ghostly figure isn't a Scottish widow, the French Lieutenant's Woman or Sister Wendy. Was the shape that brought thousands to view it on a greenhouse window in Saskatchewan in 2002 actually just a hoodie?

In the same way, whether it's on a burnt breaded fish fillet or a Google Earth image of the desert in Peru, Jesus is known by his beard, but on what basis exactly are we supposed to rule out the possibility that this is Judas or Karl Marx, Russell Brand or Hagrid?

Enthusiasts for these apparitions – who are many – talk about how they have increased their faith, but considering the phenomenal amount of faith you need to see anything in them in the first place, this seems rather unnecessary.

The principle at work here is obvious. We see so many random shapes every day that inevitably every so often the world around us will throw up something a bit anthropomorphic, but once you see it its effect can be quite striking. It's what happens when children are scared by faces in the pattern on a curtain in the dark. It's the reason there's a man in the moon and why some places and plants are named after human features. We all have a propensity to find meaning and familiarity in random patterns.

The difference is that if you believe God is in perfect control of all that happens, and that he communicates to people, then it becomes relatively reasonable to ask if that beardy shape in your pastie is God's way of telling you that he's with you in these hard times. Of course, it's also reasonable to say, "No, of course it isn't", but religious believers have no monopoly on unreasonableness, and the idea may be too comforting to be easily dismissed.

So perhaps after all, in these hard times of recession, swine flu and The Boat That Rocked, when people are asking "Where is the hand of God in this?", he has provided an answer: it's in a wall in Idaho. That would explain a lot.